Tactile sensors are widely used in various fields. Basically, they are sensors which detect intensity, a position, a direction and the like of a contact, when an object is in contact with another object. The tactile sensor is applied to a hand and skin of a robot, and is utilized as information to determine next action of the robot. In addition, the tactile sensor is utilized for detection of a sitting state on an automotive seat, a surface pressure distribution of a bed and a carpet, detection of a collision state of vehicles, detection of a motion state of organisms (for example, motion capture, detection of biological motion such as respiratory status, relaxed state of muscle), detection of intrusion into a restricted access area, foreign matter detection of a sliding door, a keyboard input device and the like. There are various proposals with respect to the tactile sensor and a method of making the tactile sensor (in Patent Documents 1 to 3).
Patent Document 1 discloses a pressure detection device comprising: a buffer member deformable by pressurizing and depressurizing including a magnet, and a sensor assembly for detecting a change in a magnetic field caused by deformation of a buffer portion with a magnetic sensor. The magnet present in the buffer member may be one large magnet (FIG. 1 of Patent Document 1) or small magnets uniformly dispersed (FIG. 7 and the like of Patent Document 1). In case of the one large magnet, there is a problem that it is difficult to detect the deformation due to touching, and a foreign body sensation is caused due to touching it. On the other hand, in case of the small magnets uniformly dispersed, since a phenomenon of canceling magnetic forces between magnet particles occurs even if the direction of the magnetic force of each magnet is the same as one another and the magnet near a contact surface moves but the magnet present inside the buffer member is difficult to move, there is a problem that detection sensitivity is poor when the external force is small and the deformation is very small.
Patent Document 2 discloses a detecting device comprising a viscoelastic magnet obtained by kneading and molding a magnet material and a viscoelastic material and magnetic-flux detecting means for detecting a change in a magnetic flux density vector due to deformation of the viscoelastic magnet. In the detecting device of Patent Document 2, since the magnet material is kneaded in the viscoelastic material, the magnet material is uniformly dispersed. Therefore, since a phenomenon of canceling magnetic forces between the magnet particles occurs and the magnet near a contact surface moves but the magnet present inside the buffer member is difficult to move, there is a problem that detection sensitivity is poor when an external force is small and the deformation is very small as described in Patent Document 1.
Patent Document 3 discloses a pressure-sensitive sensor comprising a magnetic sensor, an elastomer and permanent magnets sequentially laminated and fixed on the magnetic sensor, lead wires connected to input and output terminals of the magnetic sensor. In the pressure-sensitive sensor, since an elastic material is separated from a magnet-containing material, it is necessary to “sequentially laminate and fix” them, and there is a problem that peeling at an interface between the layers can be caused in addition to the necessity of a laminating step.
In addition, in a technical field of a robot or the other fields, for example, detection of a sitting state for an automotive, a surface pressure distribution of a bed or a carpet, detection of a collision state for vehicles, detection of a motion state of a living body (such as a motion capture, detection of a respiratory state, detection of a relaxed state of muscles and the like), trespass into a restricted area, foreign substance detection of a sliding door, a keyboard input device, it is necessary to detect a bending of an elastic body by a sensor. It is necessary to detect a bending of an elastomer corresponding to a skin of a humanoid robot, when controlling a motion of the humanoid robot and responding to an external pressure. Many sensors detecting the bending deformation and methods for making them have been proposed (Patent Documents 4, 5 and the like).
Patent Document 4 discloses deformation sensor having transparency, which is a flexible element comprising
a non-aqueous polymeric solid electrolyte containing a polymer component which is selected from a polymer containing a monomer unit having a heteroatom or a block copolymer containing a block of the polymer and an ionic liquid, and
at least a pair of electrodes,
wherein the flexible element has a total light transmittance of not less than 70% and deformation of the flexible element generates an electromotive force. It is necessary to mount the electrodes directly to the flexible element for measuring the electromotive force, and there is a problem that peeling at a bonding surface between the element and electrode is easily caused.
Patent Document 5 discloses a magnetic angle sensor which can maintain detection accuracy of the angle by preventing a magnetic dust from an invasion of a magnetic dust in a magnetic gap of the magnetic dust. Since a solid magnet disk is used, there is a problem that it has no flexibility.